Stents for prosthetic heart valves and methods of making same

ABSTRACT

A single piece stent construction having a plurality of commissure posts, each of which extends upwardly from a solid ring along a bend line and generally along a central longitudinal axis of the stent.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 U.S.C. §119(e) of U.S.Provisional Patent Application No. 61/171,193, filed Apr. 21, 2009,which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates generally to stents for use with valves,and more particularly relates to stent frame constructions.

BACKGROUND

A wide variety of stent configurations and constructions are availablefor use with stented valves, such as stented heart valves. Many of thesestents comprise wire or metal frames having a number of differentcomponents or sections that are arranged in a particular manner toprovide certain characteristics for the finished device or component.For some applications, the stents can be made from shape memorymaterials, such as Nitinol, that can be compressed to a reduced size forimplantation held in that compressed state, and then released to allowtheir expansion once they are positioned at a desired implantation site.In other applications, the stents can be compressed to a reduced size,and then expanded when desired through the use of an outward radialforce that is applied from the inner area of the stent, such as can beaccomplished with an expandable balloon. In still other applications, astent used for a stented valve may not be compressible and expandable,but may instead have fixed dimensions. In many of these applications,the stents are provided with relatively cylindrical outer shapes togenerally match the shape of the vessels in which they will beimplanted.

One method of making a stent is to start with a tube or cylinder ofmaterial having solid walls and cutting out certain portions to provideapertures and/or other structural features for the stent. For example,removing large and/or multiple portions of material from a cylinder maybe desirable to provide openings in certain areas of a stent whileproviding sufficient structure that will be conducive to compression forpercutaneous delivery. However, it can be difficult to manufacturerelatively large tubes that are made of materials such as Nitinol, andthese tubes can therefore be expensive and difficult to find. Anothermethod of making stents, such as stents having large diameters, is touse Nitinol wires arranged and attached to each other in predeterminedpatterns to make a particular structure. However, this method can betedious and also requires crimping or welding wire ends to each other toform a cylinder, which can be very labor intensive. Yet another methodof making stents involves using a flat sheet of material from whichportions of material are removed. However, this method also requires theuse of a weld seam to join the two ends of the flat sheet into a tubularstent. Although such constructions can be appropriate in somesituations, it is also understood that weld seams can be the weakestpoint in a stented valve construction. Thus, it is desirable to provideadditional methods for producing stents of various materials and mayparticularly be desirable to provide methods and configurations that donot require the use of welds or other attachment methods.

SUMMARY

The stent frames of the invention are generally provided for use with anattached valve structure to create a valved stent, which can be used asa replacement heart valve, for example. The stent frames are made from asingle piece of material, thereby eliminating weld seams that canprovide an undesirable area of weakness. The stents of the inventioninclude a wide variety of structures and features that can be used aloneor in combination with features of other stents of the invention.

Methods of forming the stent frames of the invention include cutting orstamping a stent blank from a sheet of material, or otherwise formingmolding a stent blank that is relatively flat. The stent blank can thenbe formed into a cylinder shape using heat treatment in a stepwisemethod, thereby forming a tubular stent frame. Alternatively, the stentblank can be formed into a cylinder shape using a deep forming orshaping process to form a tubular stent frame. A bioprosthesis can beattached to the wires of this stent in certain, predetermined locationsand preferably will be sewn to the wires in such a way that the material

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be further explained with reference to theappended Figures, wherein like structure is referred to by like numeralsthroughout the several views, and wherein:

FIG. 1 is a top view of an embodiment of a stent blank having a firstexemplary pattern;

FIG. 2 is a top perspective view of the stent blank of FIG. 1 formedinto a relatively cylindrical or tubular stent shape;

FIG. 3 is a top view of another embodiment of a stent blank having asecond exemplary pattern; and

FIG. 4 is a perspective view of the stent blank of FIG. 3 formed into arelatively cylindrical or tubular stent shape.

DETAILED DESCRIPTION

In accordance with the invention, forming methods are provided for usein stent construction. In particular, methods and constructions areprovided that involve heat treatment for materials such as Nitinol andsheet metal deep forming for material such as stainless steel, andparticularly involve the use of a single, integral stent constructioninvolving these types of formation methods. With these embodiments, themethods and constructions of the invention eliminate the use of welds orother forms of attachment of components in the stent construction.

Referring initially to FIGS. 1 and 2, one exemplary heart valve stentdesign in accordance with the invention is illustrated. With thisdesign, a stepwise heat treatment approach can be taken to form a stentfrom a flat sheet of material, such as a shape memory material (e.g.,Nitinol). First, a flat sheet of material is provided and apredetermined shape for the stent is cut from the material, which can beaccomplished with a stamping operation or by cutting the material with alaser, for example. As is shown in FIG. 1, a flat stent blank 10includes a central ring 12 surrounding a generally circular opening 14,and three shaped members 20 that extend outwardly from the central ring12.

In this embodiment, the shaped members 20 are spaced from each other atpredetermined locations around the central ring, each of which can beused as one of the commissures for a valve, as will be explained below.These shaped members 20 are configured to have a generally teardrop ormodified oval shape, although other shapes for the members arecontemplated. In one embodiment, each of the members 20 is spaced atapproximately 120 degrees from each adjacent member 20. However, it iscontemplated that all of the members 20 are not evenly spaced from eachother. Such a non-uniform spacing can be provided to accommodate forparticular anatomical or other structural considerations for the formedstent structure and any valves or other structures that will bepositioned in the internal stent area. It is further contemplated thatmore or less than three of such members are provided for a blank of theinvention, where the resulting stent embodiments will have more or lessthan three commissure posts or segments and can thereby accommodatevalves having more or less than three leaflets, for example.

Each of the members 20 comprises an outer frame 22 with an aperture 24defined by an inner edge of the outer frame 22. These members 20 willprovide the commissural posts for a stent frame after the formingprocess that will be described below. One or more of the members 20 canhave a single aperture 24 that is generally teardrop shaped, althoughthe aperture shape can be different, such as circular, oval, elliptical,triangular, rectangular, or the like. Each aperture 24 is shown ashaving the same relative size and shape for each of the members 20;however, the apertures 24 of a single frame can have different sizes andshapes from each other, such as can be provided to accommodate a certainconfiguration for the attachment of a valve within the interior area ofthe formed stent. One or more of the members 20 can alternatively beprovided with multiple apertures that are spaced from each other in anordered or random pattern across the face of the member. In a furtheralternative, one or more of the members 20 may be a solid piece thatdoes not have any type of aperture.

The flat stent blank 10 further includes multiple support members 30positioned between each pair of shaped members 20. In particular, eachof the support members 30 extends outwardly at a first end 32 from thecentral ring 12 so that its second end 34 is spaced from the centralring 12 by a distance that is equal to the length of the support member30. Each of the support members 30 is illustrated as a straight wireportion that extends at an angle of approximately 90 degrees relative tothe outer edge surface of the central ring 12, although it iscontemplated that the support members can be angled or curved relativeto the central ring 12.

A sinusoidal wire structure 40 also extends between each adjacent pairof members 20 and is attached to or extends from the second end 34 ofmultiple support members 30. In particular, the sinusoidal wirestructure 40 includes a series of peaks 42 and valleys 44, where thevalleys 44 of the wire structure 40 are positioned at second end 34 ofsupport members 30. Although the illustrated wire structure 40 isprovided with the same number of valleys 44 as the number of supportmembers 30 (i.e., every valley 44 corresponds with a support member 30and vice versa), it is contemplated that there can be more or lessvalleys 44 on a particular wire structure than the number of supportmembers 30 that extend from the central ring 12. In this embodiment ofthe invention, the overall distance that the shaped members 20 extendfrom the central ring 12 is larger than the overall distance that thesupport members and wire structure 40 extend from the central ring 12.However, it is understood that the relative sizes and shapes of thevarious components are only intended to be representative, and that thevarious portions of the stent blank 10 can be different from theillustrations.

The widths of the various components or members that make up the stentblank can be the same or different from each other. For example, thecentral ring 12 is shown as having a somewhat larger width than thesupport members 30 and wire structure 40. Such differences can beprovided to allow deformation of certain portions of the stent blank 10while maintaining other portions of the stent in a fixed configuration.In the embodiment of FIGS. 1 and 2, the wire structure 40 is has arelatively small width so that it can be reconfigured or deformed aparticular amount during the stent forming process while allowing for adifferent amount of deformation of the central ring 12 during this samestent forming process.

FIG. 2 illustrates the flat blank 10 of FIG. 1 after it has been formedinto a cylinder shape using heat treatment in a stepwise method to forma stent 50. That is, heat is applied to the flat piece of material in amanner that allows it to be formed into a cylinder, while stillmaintaining the material properties of the sheet. Such a heat treatmentmethod might be used when the blank is made from a material such asNitinol or another shape memory material; however, should the blank bemade from a different material, such as stainless steel, a differentheat treatment method may be used, such as deep forming. The variousstructures of the flat piece of material or blank can be heated to asufficient temperature to allow it to be reconfigured without completelychanging the shape or structure of the structures that make up theblank. That is, the shaped members 20, which will provide the commissureposts for a valve, are formed upwardly relative to the central ring 10until the shaped members 20 are generally parallel to a centrallongitudinal axis that extends through the central ring 10. At the sametime, the support members 30 and the corresponding wire structure 40extending from the support members will also be formed upwardly relativeto the central ring 10. The sinusoidal shape of the wire structure 40advantageously allows for its deformation during the forming process toaccommodate the positioning of the components. That is, the sides of thearches of the wire structure 40 can be moved toward or away from eachother without significantly altering the overall shape of the stent 50.

In an alternative embodiment, one or more of the shaped members 20,support members 30, and/or wire structures 40 can be formed so that theyat least slightly offset or angled relative to the central longitudinalaxis of the formed stent. For example, one or more of the components canbe slightly flared or angled outwardly relative to the longitudinalaxis.

After the stent 50 is formed and cooled as described above, a valvestructure can be positioned within its internal area 54. The valve canbe attached in such a way that each of its commissures is attached toone of the shaped members 20. In one example, a valve structure can besewn or adhered to the shaped members 20 in such a way that a leafletextends between each adjacent pair of shaped members 20. In a particularexample, valve tissue can be pulled through the openings 24 forattachment of the valve to the outer frame 22, where the tissue canoptionally be wrapped or partially wrapped around the outer frame 22.

The illustrated shaped members 20, sinusoidal wire structures 40, andsupport members 30 of the stent structure 50 are only one exemplaryembodiment of an arrangement that will provide sufficient structuralsupport for the stent when it is formed into its cylindrical shape. Thatis, many other structures and shapes are considered to be within thescope of the invention that would also provide such support for thestent. For example, the central ring 12 can have a shape that is notcircular, but instead is oval, elliptical, irregularly shaped, or thelike, in order to accommodate different valve configurations, forexample.

Referring now to FIGS. 3 and 4, another exemplary heart valve stentdesign in accordance with the invention is illustrated. With thisdesign, a deep forming process can be used to form a stent from a flatsheet of material, such as stainless steel. First, a flat sheet ofmaterial is provided and a predetermined shape for the stent is cut fromthe material, which can be accomplished with a stamping operation or bycutting the material with a laser, for example. As is shown in FIG. 3, aflat stent blank 110 includes three flanges 112, each of which includesa first arc portion 114 and a second arc portion 116 spaced from thefirst arc portion 114.

In this embodiment, each of the flanges 112 is defined by a firstportion 114, which also defines a portion of the outer edge of the blank110, a second portion 116 which is closer to a central area 118 of theblank 110 than the portion 114, a first edge 120 from which one end ofthe first and second portions 114, 116 extend, and a second edge 122from which the other end of the first and second portions 114, 116extend. That is, edges 120, 122 define the two sides of each flange 112,and the first and second arc portions 114, 116 extend between theseedges 120, 122. Further, the edges 120, 122 are angled away from eachother and the first portion 114 has a greater length than the second arcportion 116. Further, the flanges 112 are positioned about the centralarea 118 of the blank 110 so that one angled edge 120 of one flange 112and one angled edge 122 of an adjacent flange 112 intersect to provide aV-shaped structure that defines a V-shaped space 130 between twoadjacent flanges 112. In this embodiment, such a space 130 is providedbetween each pair of adjacent flanges 112 so that three V-shaped spacesare provided around the blank 110.

In this embodiment, each of the flanges 112 is spaced at approximately120 degrees from each adjacent flange 112. Accordingly, each of theV-shaped spaces 130 is also spaced at approximately 120 degrees fromeach adjacent space 130. This spacing of the V-shaped spaces 130 can bedefined with a radial line that is extended outwardly from thecenterpoint of the blank 110 and through the base of each V-shaped space130 such that the radial lines would each be spaced at 120 degrees fromeach other. However, it is contemplated that all of the flanges 112 arenot evenly spaced from each other on a particular blank 110. Such anon-uniform spacing can be provided to accommodate for particularanatomical or structural features for the formed stent structure and/orany valves or other structures that will be positioned within theinternal stent area, once a stent is formed. It is further contemplatedthat a blank is provided with more or less than three of such members,where such blanks will provide stent structures that have more or lessthan three commissures posts or segments, and can thereby accommodatevalves having more or less than three leaflets.

As described and illustrated, each of the flanges 112 comprises two arcportions 114, 116; however, the flanges 112 can alternatively includemore or less than two arc portions. It is further contemplated that thedifference in lengths between the arc portions can be different thanshown, which will thereby provide a different angle between the edgesthat define the V-shaped spaces 130. In addition, the entire length ofeach of the arc portions is not necessary a smooth curved shape having agenerally uniform radius, as shown, but can instead comprise alternativeshapes, such as multiple arcs connected to each other, one or more arcsconnected to one or more straight portions, and the like.

Although the base of each V-shaped space is illustrated as anintersection point between two linear edge portions, otherconfigurations are possible. For example, the base of one or more of theV-shaped spaces can include a radius or curved intersection area.

The angled edges 120, 122 may also be configured differently thanillustrated. For example, these edges can be curved or otherwiseconfigured to cooperate with the arc portions that extend between them.In another example, each of the edges can comprise a combination of oneor more curved or straight portions that extend from each other alongits length. It is noted that each of the edges 120, 122 includes aportion 120 a, 122 a, respectively that extends between the ends of twoarc portions and another portion 120 b, 122 b, respectively, thatextends from one arc portion to the base of the V-shaped space.

FIG. 4 illustrates the blank 110 of FIG. 3 after it has been formed intoa cylinder shape using a deep forming or other metal forming/shapingprocess to form a stent 150. That is, the various structures of theblank 110 are shown after they have been deep formed in a process thatallows the sheet to be shaped into a cylinder, while still maintainingthe material properties of the sheet. Such a heat treatment method mightbe used when the blank is made from a material such as stainless steel;however, should the blank be made from a different material, such asNitinol or another shape memory material, a different heat treatmentmethod may be used. The various structures of the flat sheet can beformed in such a way that the V-shaped structures and/or flanges areextending in a direction that is generally parallel to a centrallongitudinal axis of the cylindrical stent. Alternatively, one or moreof the structures of this stent can also be at least slightly offset orangled relative to the central longitudinal axis of the formed stent.After the stent is formed and cooled, a valve structure comprisingleaflets can be attached within the interior portion of the stent, ifdesired.

The illustrated V-shaped structures, spoke portions, arc portions, etc.of the stent structure are only one exemplary embodiment of anarrangement that will provide sufficient structural support for thestent when it is formed into its cylindrical shape. Thus, many otherstructures and shapes can be provided that would also provide suchsupport for the stent.

As illustrated in FIG. 4, the V-shaped structures extend upwardly insuch a way that they create commissure posts 152 between each pair ofarc portions 114, 116. The upper portion of each of these structures isdefined by the edge portions 120 b, 122 b of two adjacent flanges 112,which are the edge portions that extend beyond the arc portions 116. Oneor more of the posts 152 may be defined partially by edge portion 120 aand/or edge portion 122 a that is bent or formed inwardly toward theopposite edge portion to create a space 154 between them. Alternatively,these edge portions can touch or almost touch, thereby creating an areafor attachment or other cooperation with tissue or valve material. Inyet another alternative, the edge portions 120 a, 122 a are generally inline with the other portions 120 b, 122 b of the edges 120, 122.

The present invention has now been described with reference to severalembodiments thereof. The contents of any patents or patent applicationcited herein are incorporated by reference in their entireties. Theforegoing detailed description and examples have been given for clarityof understanding only. No unnecessary limitations are to be understoodtherefrom. It will be apparent to those skilled in the art that manychanges can be made in the embodiments described without departing fromthe scope of the invention. Thus, the scope of the present inventionshould not be limited to the structures described herein, but only bythe structures described by the language of the claims and theequivalents of those structures.

1. A tubular stent having a single-piece construction, the stentcomprising: a solid ring having a central opening; and a plurality ofshaped members extending upwardly from the ring along a bend line andspaced from each other around a circumference of the ring, wherein anouter circumference of the tubular stent comprises the plurality ofshaped members.
 2. The stent of claim 1, further comprising at least onewire structure spaced from the ring and having a first end extendingfrom a first shaped member and a second end extending from a secondshaped member that is spaced from and adjacent to the first shapedmember.
 3. The stent of claim 2, wherein the wire structure comprises asinusoidal pattern.
 4. The stent of claim 2, further comprising at leastone support member extending between the ring and the wire structure. 5.The stent of claim 4, wherein each of the support members extendsupwardly from the ring along a bend line between the ring and thesupport member.
 6. The stent of claim 1, wherein each of the shapedmembers comprises at least one aperture.
 7. The stent of claim 1,further comprising a prosthetic valve attached to each of the shapedmembers and positioned within an interior area of the tubular stent,wherein the valve comprises a leaflet extending between each pair ofshaped members.
 8. The stent of claim 1, wherein each of the shapedmembers extends in a direction that is generally parallel to a centrallongitudinal axis of the tubular stent.
 9. A tubular stent having asingle-piece construction and a longitudinal axis, the stent comprising:at least two angled members spaced from and extending generally alongthe longitudinal stent axis; at least one upper connecting memberextending between two adjacent angled members; and at least one lowerconnecting member spaced from the upper connecting member along thelongitudinal stent axis and extending between two adjacent angledmembers.
 10. The stent of claim 9, further comprising three angledmembers and three upper and lower connecting members, wherein each ofthe upper and lower connecting members extend between two adjacentangled members.
 11. The stent of claim 10, wherein a circumference ofthe tubular stent comprises the three angled members and three upper andlower connecting members.
 12. The stent of claim 9, wherein each of theangled members comprises a V-shaped portion and a second portionextending from each of the ends of the V-shaped portion, and wherein thesecond portions are moveable relative to the V-shaped portion.
 13. Amethod of forming a tubular stent having a single-piece construction,comprising the steps of: providing a generally flat stent blankcomprising a solid ring and a plurality of shaped members extendingoutwardly from the ring; applying heat to the stent blank while bendingeach of the shaped members upwardly along a bend line toward a centrallongitudinal axis that extends through a central point of the ring. 14.The method of claim 13, wherein the stent blank comprises a shape memorymaterial.
 15. The method of claim 13, wherein the stent blank comprisesstainless steel.
 16. The method of claim 15, wherein the step ofapplying heat to the stent blank comprises deep forming the stent into atubular shape.
 17. The method of claim 13, wherein the stent blankfurther comprises at least one wire structure spaced from the ring andhaving a first end extending from a first shaped member and a second endextending from a second shaped member that is adjacent to the firstshaped member, and wherein the step of applying heat to the stent blankcomprises forming the wire structure toward the central longitudinalaxis of the stent.
 18. The method of claim 17, wherein the wirestructure comprises a sinusoidal pattern.
 19. The method of claim 13,further comprising the step of attaching a valve to each of the shapedmembers within an interior area of the stent, wherein the valvecomprises a leaflet extending between each pair of shaped members. 20.The method of claim 13, further comprising the step of cutting the stentblank from a solid sheet of material prior to applying heat to the stentblank.